Piezoelectric materials

ABSTRACT

PIEZOELECTRIC MATERIALS OF A TERNARY METAL OXIDE SYSTEM COMPRISISNG 0.3 TO 20.0 MOLE PERCENT OF A(ME1/2TE1/2)O3 (WHERE A DENOTES AT LEAST ONE METAL SELECTED FROM THE GROUP OF BARIUM, STONTIUM AND CALCIUM AND ME REPRESENTS AT LEAST ONE METAL SELECTED FROM THE GROUP OF MAGNESIUM AND ZINC), 57.0 TO 35.0 MOL PERCENT OF PBTIO3 AND 55.0 TO 25.0 MOL PERCENT OF PBZRO3.

8'- 1972 NOBORU ICHINOSE ETAL 3,686,122

PIEZOELECTRIC MATERIALS Filed May 25, 1971 3 Sheets-Sheet 1 ANICAL COUPLING K33 ("/a) 01 0 \l o EEEcTRemEcH gOEFFICIENT 10.0 (MOL%) 20.0 A(Me /2Te /2)O3 50.0 45.0 (MOL%) 40.0 PbTiOs 50.0 45.0 (MOL%) 40.0 PbZr'03 FIG. 2

CAL COUPLING K33,

ELECTRO-MECHANI EOEFFICIENT O g- 22, 1972 NOBORU ICHINOSE ETAL 3,686,122

PIEZOELECTRIC MATERIALS Filed May 26, 1971 s Sheets-Sheet a A(Me /2Te /2)O3 FIG.3

g 20 40 so so 10o PbT|O3 PbZrO3 2 E z 12- O O E s- 0 LL! l LL! 6 Aug. 22, 1972 Filed May 26, 1971 ELECTRO-MECHANICAI. COUPLING VARIATIONS OF K NOBQIRU IYCHINOSE ETAL 3,686,122

PIEZOELECTRIC MATERIALS 3 Sheets-Sheet 3 I 1 g 60- V E g 20- L1. L1. O

REPETITION OF PRESSURE APPLIED (PRESSURE 3 1'ron/cm United States Patent W U.S. Cl. 252-623 1 Claim ABSTRACT OF THE DISCLOSURE Piezoelectric materials of a ternary metal oxide system comprising 0.3 to 20.0 mole percent of A(Me Te )O (where A denotes at least one metal selected from the group of barium, strontium and calcium and Me represents at least one metal selected from the group of magnesium and zinc), 57.0 to 35.0 mol percent of PbTiO and 55.0 to 25.0 mol percent of PbZrO This invention relates to piezoelectric metal oxide materials and more particularly to piezoelectric metal oxide materials of a ternary metal oxide system prepared by solid phase reaction from a plurality of metal oxides having different valances and characterized by high piezoelectric properties and excellent stability and in consequence well adapted for use as, for example, electromechanical conversion elements.

As is well known, piezoelectric materials are applied in a broad field including, for example, transducer elements for mechanical filters, elements for ceramic filters, and elements for pickups, microphones and oscillographs as well as ignition elements for gas implements. For such uses, there have been developed improved forms of piezoelectric materials comprising a binary oxide system of PbTiO -PbZrO (having a substantially equal mol percent). Attempts have been made to effect improvement by adding, for example, CdO or ZnO to said binary metal oxide system of PbTiOg-PbZrO However, said product has the drawbacks that it has an electro-mechanical coupling coeflicient K, of only 37 to 48%, and its piezoelectric properties appreciably vary with time or temperature. There have also been proposed piezoelectric materials of the ternary metal oxide system PbTiO -PbZrO -Pb (Mg Nb )O However, this ternary product generally has an electro-mechanical coupling coeflicient of about 50% at most and a mechanical quality factor Q of only 600 max. (The product whose mechanical quality factory Q indicates 568 has an electro-mechanical coefiicient of only 7.5%.) Generally speaking, piezoelectric materials are desired to have as high an electro-mechanical coupling coefficient as possible.

When piezoelectric materials are subjected, after polarization, to a strong mechanical pressure across the opposite electrodes, high voltage is generated. Therefore, these 3,686,122 Patented Aug. 22, 1972 materials can be used in various applications including the production of spark discharges across electrodes utilizing said voltage.

The properties of piezoelectric materials adapted for such applications can be evaluated by various constants generally associated therewith (for example, electromechanical coupling coefficient, output voltage coefficient, and dielectric constant). On application of a high mechanical pressure, there often arise decreases in output voltage and consequently in the electro-mechanical coupling coefficient (hereinafter designated as K which raises an important practical problem. Accordingly, piezoelectric materials should be manufactured considering not only said constants but also such declines in output voltage.

It is accordingly an object of this invention to provide very stable piezoelectric materials which, though repeatedly subjected to a pressure of 0.5 to 2 ton/cm. are least liable to decrease in piezoelectric properties, and which are capable of constantly generating a desired high voltage.

Another object of the invention is, therefore, to provide piezoelectric materials adapted to produce spark discharges for the ignition of, for example, gas implements and small capacity engines.

This invention can be more fully understood from the following detailed description when taken in connection with reference to the accompanying drawings, in which:

FIG. 1 is a curve diagram showing changes in the electro-mechanical coupling coefficient K of four kinds of piezoelectric materials prepared from a ternary metal oxide system according to this invention, where the proportions of the components of said system were varied;

FIG. 2 is a curve diagram showing changes in the electro-rnechanical coupling coefficient K of piezoelectric materials of a ternary metal oxide system according to the invention, where the proportions of Sr(Mg Te )O and Sr(Zn Te )O remained unchanged and the proportions of PbTiO and PbZrO were varied;

FIG. 3 is a triangular chart showing a range within which there should preferably fall the composition of piezoelectric materials of a ternary metal oxide system according to the invention;

FIG. 4 is a curve diagram showing the dielectric constant with respect to temperature of two examples of the invention;

FIG. 5 is a curve diagram showing the electro-mechanical coupling coefficient K with respect to temperature of the two examples of FIG. 4; and

FIG. 6 is a curve diagram showing changes in the electromechanical coupling coeflicient K with respect to repeated applications of pressure, as compared between three other examples of the invention and two reference samples of the prior art piezoelectric materials.

The piezoelectric material of the invention is prepared by solid phase reaction from a plurality of metal oxides having different valences, namely, by substituting part of a binary metal oxide system of PbTiO -PbZrO with A(Me Te )O of perovskite structure (where A is at least one metal selected from the group of Ba, Sr and Ca, and Me is at least one metal selected from the group of Mg and Zn), thus constituting a ternary metal oxide System of A(Me Te )O -PbTiO -PbZrO The piezoelectric metal oxide material of the invention is characterized in that it consists of 20.0 to 0.3 mol percent of A(Me Te )O 57.0 to 35.0 mol percent of PbTiO and 55.0 to 25.0 mol percent of PbZrO (the proportions of these three components are so chosen as to total 100 mol percent).

The aforesaid piezoelectric metal oxide material of the invention can generally be easily manufactured by the known powder metallurgical process. For illustration, there are accurately Weighed out the prescribed proportions of raw metal oxides such as A0, TiO ZrO TeO and MeO (where AzBa, Sr, Ca; Me:Mg, Zn). They are thoroughly mixed, for example, in a ball mill. The raw materials may also consist of hydroxides, carbonates or oxalates of metals or the like which can be thermally converted to oxides. The mixture is prefired at a temperature of, for example, about 600 to 900 C. and pulverized again in a ball mill to obtain powders controlled to a particle size of about 1 to 2 microns. To said powders is added a binder such as water or polyvinyl alcohol, and the resulting mass is made into a fiat body at a pressure of about 0.5 to 2 ton/cm. and further sintered at a temperature of about 1000 to 1270 C. Since PbO, one of the components, tends to be evaporated off during this sintering, the operation is performed in a closed furnace. The sufiicient time during which the mass should be maintained at a. maximum temperature generally ranges between 0.5 and 3 hours. Said flat sintered body of metal oxides is polarized by fitting a pair of electrodes to both sides thereof, for example, by baking silver layers therein and impressing across the electrodes a voltage having a DC. field intensity of to kv./cm. for about one hour in silicone oil at a temperature of about 140 to 160 C.

The proportions of A(Me Te )O PbTiO and PbZrO are limited as described above for the following reasons. If the content of A(Me Te )O increases over 20.0 mol percent, a piezoelectric material having an electro-mechanical coupling coefficient K of required for piezoelectric ignition can not be obtained. For instance, when there was determined the electro-mechanical coupling coefficient K of a piezoelectric metal oxide material by varying the proportions of its components: A(Me Te )O PbTiO and PbZrO there was observed the tendency shown in FIG. 1. Where the amount of A(Me Te )O fell outside of the range of 20.0 to 0.3 mol percent, the resultant product did not have the desired piezoelectric properties. In FIG. 1, the curve (a) represents the case of A:Ba and MezMg; the curve (b) the case of AzBa and Me:Zn; the curve (c) the case of AzCa and MezMg; and the curve (d) the case of A:Sr and Me:Zn.

The reason why the proportion of PbTiO is limited to the range of 57.0 to 35.0 is that either below 35.0 mol percent or above 57.0 mol percent, there can not be obtained a piezoelectric material having a large electromechanical coupling coefiicient K For example, where there were determined the piezoelectric properties of a piezoelectric material with the proportion of fixed and the proportions of PbTiO and PbZrO varied, then there was observed the tendency shown in FIG. 2. The curve (e) denotes the case of Me:Mg and the curve (f) the case of Me:Zn. As apparent from FIGS. 1 and 2, where the content of PbTiO fell to below 350 mol percent, a piezoelectric material having the required properties was not produced. Where said content rose above 57.0 mol percent, the resultant product did not have desired piezoelectric properties or was not satisfactory in respect of stability, though said piezoelectric properties themselves did not pose any problem from the practical standpoint. Therefore, the proportion of PbTiO should always be selected from the aforementioned range. Further, the remaining component PbZrO of the basic composition of A(Me Te )O -PbTiO -PbZrO should be used in amounts falling within the range of 25.0 to 55.0 mol percent in order to obtain desired piezoelectric properties. The proportions of the three components should be defined within the hatched region of FIG. 3 showing a ternary metal oxide system. The component of A(Me Te O concurrently acts as a sort of mineralizer to facilitate sintering. This ease of sintering eventually reduces required temperature to restrict the evaporation of PbO, a component of the basic composition, thus enabling a compact piezoelectric material to be finally manufactured.

As mentioned above, the piezoelectric oxide material of this invention mainly consists of a uniform solid solution of A0, TiO ZrO TeO and MeO and is of perovskite structure (as confirmed by X-ray analysis). Where the composition is expressed by the general formula ABO then A denotes divalent Ba, Sr and Ca, and B represents divalent Me, hexavalent Te and tetravalent Ti and Zr. The piezoelectric material of this invention is composed of a plurality of elements having different valences and is essentially different from the prior art piezoelectric material mainly consisting of octahedral oxygen, wherein, if the composition is expressed by the general formula of A"B"O B" represents tetravalent elements, when A" denotes divalent elements or B" represents pentavalent elements, in case A" denotes monovalent elements, that is, A" and B" respectively consist of a combination of elements having the same valence. Thus the piezoelectric material of this invention not only has excellent piezoelectric properties which little vary with time or temperature, but also always exhibits a specified performance.

Where determination was made of changes in the voltage in which piezoelectric materials used as ignition elements generated on impact, the conventional product of a binary PbTiO -PbZrO system exhibited a 15% decrease in output voltage at a millionth time of impact. In contrast, the piezoelectric material of this invention only exhibited a 5% decline in output voltage under the same condition.

Since reduced output voltage observed in the durability or pressure test of piezoelectric materials used as ignition elements eventually results in a decline in the reliability of ignition, the product of this invention may be considered highly advantageous in practical application.

The invention will be more fully understood by reference to the examples which follow.

There were accurately weighed out AO, TiO ZrO TeO and MeO so as to form 0 to 22 mol percent of A(Me Te )O 24 to 57 mol percent of PbTiO and the remaining portion of PbZrO The mixture was pulverized to a particle size of 1 to 2 microns in a ball mill and prefired at a temperature of 850 C. There were also prepared reference samples of the prior art piezoelectric materials by subjecting the raw materials to the same treatment. Thus there were provided eighty-one powdered samples of both the present invention and prior art. To the samples was added polyvinyl alcohol as a binder. The resulting mass was subjected to a pressure of 1 ton/cm. and heated one hour at a temperature of 1000 to 1280" C. to be sintered, to produce discs 1 mm. thick and 13 mm. in diameter and round rods 7 mm. in diameter and 15 mm. long.

The discs obtained were tested to determine specific gravity. Both discs and rods were polarized by applying voltage having D.C. field intensity of 30 kv./cm. one hour in silicone oil at C. and determined for piezoelectric properties by the standard method set forth in the Proceeding of IRE (vol. 137, pp. 1378l395, 1949). The results are presented in Table 1 together with the compositions of the sintered samples. Referring to Table 1, FT. represents sintering temperature C.), D,

specific gravity (at 23 C.), e, dielectric constant (1 kilo eificient (percent), the table also reports the decrease HZ. at 23 C.) and K electromechanical coupling coin K at the millionth time of impact.

TABLE 1 A(M0 T0 -0 P155010. 1 02103 Decrease Test Ina- (11101 (11101 M01 in K33 terials percent) percent) A M0 percent; F.I. D 6 K33 (percent) Reference:

00. 0 40. 0 0 1, 280 7. 41 853 40. 0 20. 8 00.0 30.0 Ba M 10.0 1,200 7.48 000 40.3 11.8 00.0 30.0 01 Zn 10.0 1,200 7.51 000 47.7 13.4 00.0 20.0 Ca M 20.0 1,240 7.40 842 44.0 12.5 00.0 20.0 Ba Zn 20.0 1,240 7.45 831 43.5 10.7

57.0 42.7 Sr Zn 0.3 1,270 7.50 072 50.4 4.0 57.0 42.7 M 0.3 1,270 7.52 033 50.2 3.0 57.0 42.7 B3 M 0.3 1,270 7. 51 084 50.3 4.0 57.0 30.0 B5 M 7.0 1,250 7.58 1,248 54.0 2.7 57.0 30.0 Sr Zn 7.0 1,250 7. 00 1,205 53.8 2.0 57.0 30.0 05 M 7.0 1,250 7.01 1,203 52.2 3.1 57.0 30.0 B0. Zn 13.0 1,220 7.02 1,451 55.8 3.0 57.0 30.0 0 M 13.0 1,220 7.01 1,518 54.0 3.3 57.0 30.0 C0. Zn 13.0 1,220 7.50 1,400 53.3 2.0 57.0 25.0 Ba M 18.0 1,200 7.55 1,310 50.0 1.5 57.0 25.0 81 Zn 18.0 1,200 7.54 1,287 50.3 1.3 57.0 25.0 Ca M 180 1,200 7.52 1,184 50.1 0.8 50.0 40.5 133. Zn 0.5 1,240 7.50 1,001 51.5 2.0 50.0 40.5 Sr M 0.5 1,240 7.55 1,043 52.0 2.4 50.0 40.5 Ca Zn 0.5 1,240 7.57 1,058 51.7 3.0 50.0 44.0 Ba M 0.5 1,210 7.02 1,503 05.4 3.5 50.0 41.0 Sr Zn 000 1,210 7.04 1,080 08.1 4.0 50.0 44.0 03 M 0.0 1,210 7.05 1,400 04.0 3.2 50.0 30.0 B3 M 14.0 1,100 7.03 1,735 03.4 2.8 50.0 30.0 Sr Zn 14.0 1,100 7.00 1,811 02.0 2.7 50.0 30.0 Ca M 14.0 1,100 7.02 1,543 01.8 2.5 50.0 30.0 Ba M 20.0 1,170 7.55 1,321 51.4 1.8 50.0 30.0 Sr Z11 20.0 1,170 7.50 1,480 50.0 1.0 50.0 30.0 05 Zn 20.0 1,170 7.54 1,300 50.7 1.5 45.0 54.5 Ba Zn 0.5 1,220 7.58 1,074 54.1 1.7 45.0 545 B0. M 0.5 1,220 7.57 1,083 53.0 2.0 45.0 54.5 Sr Zn 0.5 1,220 7.55 1,115 55.2 2.1 45.0 54.5 8; M 0.5 1,220 7.57 1,181 54.0 1.0 45.0 54.5 C3. Zn 0.5 1,220 7.54 1,018 52.0 1.4 45.0 54.5 Ca M 0.5 1,220 7.55 1,000 52.8 1.3 45.0 47.0 B3 M 8.0 1,180 7.08 2,115 72.2 3.8 45.0 47.0 Sr Zn 8.0 1,180 7.05 2,310 71.5 3.5 45.0 47.0 g3 1 811,180 7.00 2,002 70.0 3.1

a I p- 45.0 47 0 4.0 I 1,180 7. 70 2,418 74.0 4.0 45.0 47 o f 1,180 7. 00 2,385 73.3 2.0 45.0 47 0 {5; 1,180 7. 04 2,103 72.5 3.2

Ba Zn 4.0 45 0 47 0 S 1 1 1,180 7.71 2,514 75.4 2.8

a: 11 45.0 43.0 B3 M 12.0 1,100 7.00 2,240 08.8 2.0 45.0 43.0 Sr 11 12.0 1,100 7.08 2,310 07.0 2.4 45.0 43.0 00 Zn 12.0 1,100 7.07 2,084 08.1 2.5 45.0 43.0 Ba Zn 0.0 1,100 7.00 2,347 70.4 2.2 45.0 37.0 B5 Zn 18.0 1,140 7.00 1,775 57.3 1.5 45.0 870 Sr Mg 18.0 1,140 7.03 1,843 58.1 1.3 45.0 37.0 41 Z 11 1 .1 1 1,140 7.02 1,501 54.0 1.1

a g 45.0 37.0 {gr Z 11 g 1,140 7.04 1,708 50.8 1.0

a l g 40.0 55.0 Ba Zn 5.0 1,200 7.50 1,007 51.4 1.8 40.0 55.0 Sr M 5.0 1,200 7.53 080 52.1 1.4 40.0 55.0 Ca Zn 5.0 1,200 7.55 050 51.0 1.2 40.0 50.0 133. M 10.0 1,170 7.58 1,530 05.8 2.4 40.0 50.0 81 Zn 10.0 1,170 7.57 1,403 00.4 2.1 40.0 50.0 Ca M 10.0 1,170 7.55 1,384 05.1 2.0 40.0 450 B5 Zn 15.0 1,150 7.51 1,042 57.3 1.7 40.0 45.0 Sr M 15.0 1,150 7.50 1,582 58.1 1.8 40.0 45.0 02 Zn 15.0 1,150 7.53 1,400 55.0 1.8 40.0 40.0 B5 M 20.0 1,130 7.48 1,215 52.3 1.1 40.0 40.0 S1 Zn 20.0 1,130 7.40 1,188 53.1 1.2 40.0 40.0 50 l v r 2 .3 1,130 7.47 1,004 50.0 0.0

a g 40.0 40.0 IZYIg g 1,130 7. 50 1,200 53.5 0.8

51. n 35.0 55.0 Ba Zn 10.0 1,100 7.40 1,182 51.4 1.3 35.0 55.0 81- M 10.0 1,100 7.50 1,141 52.0 1.5 35.0 55.0 C3. Zn 10.0 1,100 7.51 1,100 51.1 1.0 35.0 55.0 2'8 1,100 7. 52 1,174 52.5 0.8 35.0 51.0 Ba Zn 14.0 1,140 7.55 1,348 54.5 1.4 35.0 51.0 B5 Zn 14.0 1,140 7.54 1,205 53.0 1.3 35.0 51.0 81 M 14.0 1,140 7.53 1,284 53.8 1.3 35.0 51.0 21 Z n 1 11140 7.54 1,250 53.4 1.2

r g 35.0 51 0 Zn m 1,140 7.50 1,301 54.2 1.0 5,0 510 Ca M 14.0 1,140 7.52 1,217 52.0 1.1 35.0 51 0 83 Z n 14.0 1,140 7.53 1,105 52.1 1.0

a 7.0 35.0 51 0 5 m 1,140 7. 55 1,243 53.0 1.2 470 B3. Zn 18.0 1,120 7.51 1,111 51.7 0.7 35.0 470 Sr M 18.0 1,120 7.50 1,082 52.0 0.0 35.0 470 3 l vr 12. 1,120 7.50 1,008 51.0 1.0

IBIlCe: Refe 34.0 57 0 B3. Zn 0.0 1,100 7.43 1,013 3 5.8 54.0 24 0 Sr Zn 22.0 1,170 7.48 1,147 48 0 0.2

Where determination was made of changes with temperature in the dielectric constant of Example 14 (Curie point 350 C.) and Example 49 (Curie point 310 C.), then there was observed the tendency shown in FIG. 4. The curve (g) represents Example 14 and the curve (h) Example 49. Where determination was made of changes with temperature in the electro-mechanical coupling coefficient K of Examples 14 and 49, there were obtained the results of FIG. 5. The curve (i) represents Example 14 and the curve (j) Example 49. As apparent from FIG. 5, both test materials presented little variation in the electro-mechanical coupling coefiicient K over a temperature range of -100 to 200 C. due to the high Pb(Tio 47ZI' 53)O +1.0 Wt. percent Nb205 represented by the referential sample oz.

TABLE 2 Number of impact Milli- Decrease Test 1st 1,000th 10,000th 100,000t11 eonth in materials time time time time time voltage Example 16 15.8 15. 7 15. 6 15. 4 15.2 3. 8 Example 33 16.0 16.0 15.9 15.8 15.6 2.5 Example 53 15.3 15.3 15.3 15. 2 14. 9 2. 6 Reference a 15.5 15.0 14. 3 13.7 13.0 15.6

Table 2 above proves that the piezoelectric metal oxide materials of this invention have superior properties.

Where determination was made of changes in K of elements prepared from piezoelectric materials having corresponding compositions to those of Examples 4, 25 and 34, as well as from the conventional compositions by subjecting them to repeated applications of a pressure of 1 ton/cm. then there were obtained the results of FIG. 6. As seen from FIG. 6, the elements corresponding to Examples 4, 25 and 34 only presented a decline of less than 10% in output voltage, whereas the elements prepared from the prior art piezoelectric materials having compositions of Pb(Ti Z .54) 0 +0.7 wt. percent Nb O represented by Reference 6 and represented by Reference 7 exhibited a large decrease of many percent. In FIG. 6, the curve (k) denotes Example 4, the curve (1) Example 25, the curve (m) Example 34, the curve 5 Reference 13 and the curve 'y Reterence 7.

As mentioned above, the piezoelectric materials of this invention have excellent properties which indicates little variation with time or temperature as proven by the tests, and consequently can display superior performance characteristic as transducer elements such as piezoelectric ignition elements, offering many industrial advantages.

What we claim is:

1. Piezoelectric metal oxide materials having a composition of 0.3 to 20.0 mol percent of A(Me Te )O where A is at least one metal selected from the group of Ba, Sr and Ca, and Me is at least one metal selected from the group of Mg and Zn, 57.0 to 35.0 mol percent of PbTiO and 55.0 to 25.0 mol percent PbZrO wherein the sum of A(Me Te )O PbTiO and PbZrO equals 100 mol percent.

References Cited UNITED STATES PATENTS 3,268,453 8/1966 Ouchi et al. 25262.9 3,309,168 3/1967 Bayer 252-62.9 X 3,463,732 8/1969 Banno et al. 25262.9 3,468,799 9/1969 Kurihara et al. 2S262.9

OTHER REFERENCES Bayer: Journal of the American Ceramic Society, vol. 46, No. 12, December 1963, pp. 604-5.

TOBIAS E. LEVOW, Primary Examiner J. COOPER, Assistant Examiner U.S. Cl. X.R. 10639 R 

